The invention relates to material handling equipment such as excavators and backhoes and clamping and grappling equipment used with material handling equipment and, more particularly, to a thumb assembly for use with such equipment.
The use of a thumb on material handling machinery is well known. While a thumb may be used with other implements, such as a rake, a thumb is commonly used in conjunction with a bucket on an excavator to make the bucket more effective in picking up material. For example, at demolition sites a thumb in conjunction with a bucket is a particularly useful means of handling material, such as concrete, lumber or pipe, which would be too large or otherwise difficult to be picked up solely by the bucket.
A thumb typically comprises a thumb frame which is pivotally attached to the underside of an excavator's stick and a link extending between the thumb frame and the stick to secure the thumb frame in position. The thumb frame is commonly of modular construction comprising a thumb body which is arranged for pivotal connection to the underside of the machine's stick and a tooth bar which is attached to the thumb body. The tooth bar is commonly configured to suit a particular bucket with which it will be used and typically comprises a number of teeth arranged to intermesh with teeth arrayed on the lower edge of the bucket.
When not in use, the thumb frame is typically pivoted to a stored position somewhat parallel and adjacent to the underside of the excavator's stick. From this position, the thumb frame can be pivoted relative to the stick to a working position where material can be clamped between the thumb frame and the implement. A link between the stick and the thumb frame secures the thumb frame in the stored position and in one or more working positions. Manual thumbs include a rigid or manually telescoped link between an anchor secured to the underside of the stick and the thumb frame enabling the thumb frame to be secured in the stored position and one or more working positions where material may be grasped by curling the bucket toward the thumb frame projecting from the underside of the stick. Connecting the stick and the thumb frame with a linear hydraulic actuator enables pivoting of the thumb frame from the stored position to an infinite number of working positions enabling material to be grasped by pivoting the thumb frame as well as by curling the bucket. In addition, the thumb frame can be pivoted throughout at least a portion of the bucket's movement to continue grasping material as the bucket is uncurled toward the unloading position.
However, the hydraulic thumb actuator on the underside of the stick is exposed to damage as a result of overtravel of the thumb frame in the stored and extended positions. To minimize interference with the use of the excavator it is desirable that the thumb frame be stored close to the stick which places the thumb frame in close proximity to the thumb actuator. Movement of the bucket and/or contact between the thumb frame and the surroundings can cause damaging contact between the thumb frame and the thumb actuator. On the other hand, as the thumb frame is pivoted toward the bucket by extension of the thumb actuator the rod of the actuator approaches the underside of the stick and overtravel of the thumb frame, for example, as a result of contact with the surroundings, can cause damaging contact between the actuator's rod and the stick. One or more, mechanical stops may be attached to the underside of the stick to prevent contact between the thumb frame and the thumb actuator but the additional welding and weld preparation which may include removing parts attached the stick, and the need to precisely locate the stop on the stick complicates the installation of a stop to protect the thumb actuator. What is desired, therefore, is a hydraulic thumb incorporating a mechanical stop to protect the thumb actuator which does not require welding or precise positioning on the stick.